Gasification reactors are known which are constituted in principle by a combustion chamber into which is injected a combustion supporting gas, generally oxygen, which burns a coal-based fuel mixture. In this type of method, for various reasons, the enclosure is often kept at a considerable pressure, for example of the order of 10 to 80 bars.
The coal must be finely powdered and in a known method, to convey it and inject it into the reactor, it is suspended in a liquid, generally water. In this way a pumpable mixture is obtained, but the pumps customarily used normally require a high content of liquid, higher than 40%, which does not improve the thermal efficiency of the reaction. It is true that the latter must not proceed at too high a temperature and that it is necessary in any case, in controlling this temperature, to use water as a moderator. However, the water content necessary for the gasification reaction to function well does not exceed 15%. It is therefore of interest to attempt to reduce the water content of the fuel mixture thus introduced into the reactor.
Another problem arises from the pressure existing in the combustion chamber and the need to maintain fluid-tightness therein during the introduction of the fuel. This result can be achieved when a pump is used enabling the mixture to be introduced into the vessel at the desired pressure. However, as has just been stated, a pump can only operate with a fairly high water content.
To introduce a drier mixture, it is also possible to use to piston system but such a system has the drawback of operating discontinuously.
It has also been proposed to use a screw conveyor which enables the production, by extrusion at the entrance into the combustion chamber, of a compressed plug of material sufficiently fluid-tight at the pressure of the chamber and which is renewed continuously progressively with its introduction. In known installations, this device comprises a screw rotated within a sleeve provided with an entrance for the mixture at an upstream end, and an exit opening into the pressurized vessel at a downstream end. The mixture introduced at the entrance of the sleeve is driven by the rotation of the screw to its downstream end provided with a convergent section followed by a die which retards the material to oblige the latter to be compressed so as to form, in the die, a compact plug introduced into the combustion chamber constituting the gasification reactor and continuously revewed by the material arriving from upstream.
Such a device enables the introduction into the vessel of the reactor, while maintaining fluid-tightness, of a mixture having a water content below that needed for pumping by conventional means. However, in practice, this water content must be higher than 20% and preferably of the order of 40% for a powdered material.
On the other hand, in the supply methods used to date the fuel mixture received at the entrance of the reactor generally has a fairly high water content.
In fact, to bring the fuel from the place of production or the unloading port to the place of utilization, situated sometimes at a considerable distance, it is advantageous to use a "carboduc" in which the previously powdered coal is carried in a water suspension. The water content is then very high, of the order of 90%.
It is also possible to receive the coal separately and to subject it to dry grinding. However, if it is desired to avoid too large a production of dust, the dry grinding cannot be very thorough and must be following by wet grinding.
By way of example, there is shown in attached FIG. 1 a prior art feed installation.
In this figure, there is shown diagrammatically the gasification reactor constituted by the pressurized vessel 1 at the upper part of which is located a burner 2 into which at 21 the fuel mixture is introduced, the oxygen being injected at 22.
The fuel mixture constituted by solid coal arriving at 3 is mixed, after possible dry grinding at 31, with the water arriving at 32. The mixture is introduced into a wet grinder 4 in which the grinding must be fairly thorough in order that the material emerging at 21 should not contain particles larger than the limit allowed for gasification; in practice, this limit is of the order of 0.5 millimeter.
To be introduced into the burner 2, the wet mixture emerging at 41 from the grinder passes first into a homogenization device 43 into which it is injected at 41 by a pump 44.
Even when a screw introduction device is used, the supply diagram is similar and, in particular, it is necessary to carry out very thorough grinding which, of course, increases the energy consumption of the installation.